A polyester such as aromatic polyester, aliphatic polyester, wholly aromatic polyester, semi-aromatic polyester and polycarbonic acid ester has been conventionally produced by polycondensing a petroleum-derived raw material. However, in view of recent concerns about fossil fuel depletion and global-scale environmental problems such as increase in carbon dioxide in the air and in addition, with the growing call for establishment of a circulation-type (sustainable) society, in regard to the polyester as well, practical application of a polyester using, as the raw material diol or dicarboxylic acid, a material derived from biomass resources such as plant and furthermore, a biomass plastic using the polyester, is advancing. When an yearly renewable plant is used as the raw material, the raw material supply can be irrelevant to the fossil fuel depletion and moreover, because of carbon dioxide absorption for plant growth, a great contribution to the reduction of atmospheric carbon dioxide can be afforded.
Out of polyester feedstocks, as to a dicarboxylic acid such as succinic acid and adipic acid, various methods for the production from glucose by using a fermentation process are known, in addition to the conventional chemical process. With respect to a diol as well, there are known, for example, a method of obtaining 1,4-butanediol (hereinafter, sometimes simply referred to as “1,4BG”), 1,3-propanediol, ethylene glycol, etc. by directly fermenting the biomass resource such as plant in bacterial cells, and a method of producing a carboxylic acid in bacterial cells from biomass resources such as plant by a fermentation process and then hydrogenating the dicarboxylic acid with the aid of a reducing catalyst to obtain a diol (Non-Patent Document 1).
In addition, out of polyurethanes produced on an industrial scale, a polyurethane of a polyester polyol type where the soft segment is typified by a dicarboxylic acid-based polyester, is obtained by reacting a polyester polyol and an isocyanate compound, and the polyester polyol is produced using a diol and a dicarboxylic acid derivative as raw materials and therefore, can similarly produced from a plant-derived raw material.
A polyester containing a diol in the constituent units is industrially very useful. In particular, a polybutylene terephthalate (hereinafter, sometimes simply referred to as “PBT”) that is a representative engineering plastic among thermoplastic polyesters is excellent in easiness of molding process, mechanical properties, heat resistance, chemical resistance, aroma retentivity and other physical and chemical properties and therefore, is widely used for an injection molded article such as automotive component, electric/electronic component and precision equipment component. In addition, the polyester has recently found a widespread application also in the general consumer appliance field such as film, sheet, monofilament and fiber by making use of its excellent properties and in turn, PBT with good color tone is being required.
Alternatively, an aliphatic polyester such as polybutylene succinate (hereinafter, sometimes referred to as “PBS”) and polybutylene succinate adipate has biodegradability that is a property of biograding the polymer into carbon dioxide and water with microorganisms in soil or water. Such a polyester is produced at present by polycondensing a raw material derived from fossil fuel resources, and a technique for deriving a raw material of the polyester from renewable biomass resources is expected to become very important in the future. With respect to this biodegradable polyester as well, a polymer having good color tone is required due to a recent spread of demand over various fields.
Furthermore, the above-described polyurethane of a polyester polyol type has a feature of being excellent in the heat resistance, weather resistance, etc. and is applied to a wide range of uses.
Among these polyesters, PBT is usually produced by reacting a terephthalic acid or an alkyl ester thereof with 1,4BG, and when 1,4BG as the raw material is obtained from biomass resources, PBT is deteriorated in the color tone compared with a polymer obtained from a fossil fuel such as petroleum. The main causes of this deterioration in color tone include the presence of a nitrogen atom-containing component in PBT.
For example, Patent Document 1 describes a technique for obtaining a polyester by using biomass resources as the raw material, where a polyester having a nitrogen content of 1,000 ppm by mass or less is obtained by controlling the nitrogen content in the raw material dicarboxylic acid.
Also, Patent Document 2 describes a technique for obtaining PBT by using biomass resources as the raw material, where PBT having a nitrogen atom content of 50 ppm by mass or less is obtained by controlling the nitrogen atom content in the raw material 1,4-butanediol derived from biomass resources to a range of 0.01 to 50 ppm by mass. Furthermore, it is stated that 1,-acetoxy-4-hydroxybutane (hereinafter, sometimes simply referred to as “1,4HAB”) in 1,4BG retards the polycondensation reaction of PBT and thereby causes coloring in the obtained PBT but when 1,4BG having a controlled nitrogen atom concentration is used as the raw material, coloring of PBT due to retardation of the polymerization can be reduced.
However, this patent document neither discloses nor suggests that a specific carbonyl compound in 1,4BG greatly affects the color tone of the obtained polyester, and moreover, is silent on the content of the specific carbonyl compound having a great effect on the coloring.